Veal bones can be found at most grocery stores like Whole Foods, butchers and other meat-related businesses.
Rinse veal bones in cold water and put them in a 24qt/25L stockpot. Fill the pot with twice as much cold water as you have the bones. Bring to a simmer on medium high. As the liquid is being brought to a simmer, move the bones around from time to time. Skim off the scum that rises to the surface and remove the pot from the heat. Do not boil. Drain bones in the sink or in a large colander and rinse with cold water to stop cooking process and remove any scum. Clean the stockpot to remove any impurities.
Returns the bones to the cleaned stockpot. Fill the pot with cold water, adding more than twice as much water as you have bones. Bring water to a simmer on medium high heat. This will take about 90 minutes. Skim every so often (it is easier to skim before the aromatics are added). Once the liquid is at a simmer, stir in the tomato paste (Omit tomato paste if making white veal stock). Add the mirepoix and tomatoes. Bring back to a simmer and simmer for 6 hours; uncovered. Skim off impurities during the cooking process. Remove bones using a spider and strain the veal stock in a stainless steel bouillon strainer or sieve. Save the bones if making another batch (Remouillage). Do not press on solids. Chill stock, refrigerate and freeze. Refrigerate for up to 1 week or freeze for up to 6 months.
Continue to simmer veal stock for 8 hours more; 14 hours total. Remove bones using a spider and strain the demi glace in a stainless steel bouillon strainer or sieve into a smaller pot. Save the bones if making another batch (remouillage). Do not press on solids. Bring to boil and simmer for 2 hours. Skim off remaining scum and fat from the surface. Stock should yield 3 Qt/3L of demi glace. Cool it quickly by placing the pot in a sink half filled with ice water. To cool it faster, whisk it every 5 minutes or so. Once at room temperature, refrigerate or freeze demi glace into desired portions. Refrigerate for up to 2 weeks or freeze for up to 10 months.
Repeat the Veal Stock 1 recipe steps, and simmer stock for 8 hours. It should yield 8 Qt/8L. Remouillage (Remy) is a weak stock made by re-simmering bones that have been used to make stock once already. Not as good and rich than the first extraction but remouillage can be used for less demanding preparations. Remouillage can also be used as a replacement for water or part of it during your next preparation of veal stock or demi glace. It produces much more enhance flavor.